# 1_ Lewis Dot Diagrams

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```					Lewis Dot Diagrams
Try Nitrogen and Gallium
1) Lewis Dot Diagrams
 another way to show electron
configuration

G. N. Lewis
 also allows us to   visually represent
1875 - 1946
bonds and molecule shape
 named after G.N. Lewis
1) Lewis Dot Diagrams
 diagram creation

Cl
 write the atomic symbol
 imagine 4 orbitals around the symbol
each orbital can hold 2 e- (max)
 put dots in, to represent valence e-
put one electron In each orbital before
doubling up
 # dots = # valence electrons
1) Lewis Dot Diagrams
Electrons are divided between core and valence
electrons
for Lewis Dot Diagrams:
valence e- are only those in the
highest principle quantum number

B - 1s2 2s2 2p1
valence = 2s2 2p1

Br [Ar] 4s2 3d104p5
Br
valence = 4s2 4p5
this way Lewis Dot Diagrams will normally have 8 e- (ie, dots) max
1) Lewis Dot Diagrams
recall:
 Atoms like to either empty or fill their
outermost level.
 Since the outer level contains two s
electrons and six p electrons (d & f are
always in lower levels), the optimum
number of electrons is eight.
 This is called the octet rule.
1) Lewis Dot Diagrams
 examples
O

O   O
H

He

 Ne
1) Lewis Dot Diagrams
 vocab:
a lone pair of e-
or just
“lone pair”

O
bonding electrons

note: all of the dots are valence e-

 so…oxygen has 2 lone pairs and 2
bonding electrons (6 valence e-)
2) So What?
 drawing atoms in this way helps us
understand covalent bonds

recall:
covalent bonds - sharing of e-
ionic bonds - transfer of e-

 these diagrams are not as useful with ionic
bonds
 ions in ionic bonds already have full octets
 Lewis diagrams would be pretty boring
2) So What?
 we call them “bonding electrons” for a reason

Cl needs 1 more e-
 consider:

H                          Cl
H needs 1 more e-
 how many e- does H need to be “happy”?

 these two “unhappy” atoms can work together to
both be “happy” by SHARING their bonding e-!
2) So What?

H                           Cl
electrons in different “unhappy” atoms will rearrange
themselves, and form bonds to become “happy”!

H Cl
H is happy                                Cl is happy
it has 2 e-                               it has 8 e-
 notation note:
 to show where the e- originally came from, we often
use x’s and o’s to distinguish between electron origin

H Cl = H Cl                    x

 we also show the e- between atoms (the bonding e-
) as a line

H- Cl
shared or bond pair e-

This is the the LEWIS STRUCTURE of HCl.
3) Steps to Build a Lewis Structure
1. Draw the lewis stucture of the central atom
(normally the “single” atom)

N
1 Ns in NH3                                 3 Hs in NH3

N is the central atom
3) Steps to Build a Lewis Structure
2. Draw the other atoms around the central one

H   x         N               H      x

H   x

2. Start pairing up the electrons   (using circles or lines)
3) Steps to Build a Lewis Structure
4. Carefully redraw the bond pairs as lines.

H   x         N           H   x

H   x

5. If needed, move electrons around to keep
octets (more on this later)
NOTE:
H N H x
x
x

H            a bond is just a pair
of electrons

 NH3 has 3 bond pairs and 1 lone pair
of e-

 notice: each atom is now “happy”
each H has 2 e- and the N has 8 e-
Try It!
 Draw the Lewis dot structure for:

H2O
be sure to follow the steps!
CH4
Homework
page 244:
#1-5

Draw the Lewis Structure for:
H2O2                       each atom has an octect

CO2

```
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 views: 25 posted: 2/11/2012 language: English pages: 17